Golf ball

ABSTRACT

A golf ball has plural dimples provided on a surface of the golf ball; a first land part existing between the plural dimples and having as its surface a spherical surface of a sphere having the center of the golf ball as its center; a second land part having a boundary with the first land part or boundaries with the first land part and the plural dimples and having a surface having a smaller curvature than the spherical surface of the first land part; and an engraved marking disposed substantially on the second land part.

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball having an engraved marking.

Markings such as symbols, numerals, letters, and patterns are often applied to the surfaces of golf balls. Methods of applying such markings to the surface of a golf ball include methods of printing or transferring ink onto the surface of the golf ball and methods of engraving on the surface of the golf ball.

Because plural dimples are disposed at high density on the surface of a golf ball, the former method has a problem of a tendency for produce poor printing. With the latter method, there is a problem of difficulty in engraving a marking, such as a logo, having a complex shape. Also, because the edges of the recessed part are sharply pointed, there is the problem of an adverse affect on the aerodynamic characteristics of the golf ball.

U.S. Pat. No. 7,303,492 discloses a golf ball in which dimples are made into the shape of text letters or characters or other symbols. When a symbol is constituted by dimples, however, the symbol itself becomes very large, and in order to mark the surface of the golf ball with the desired symbol, there is a problem of an excessively large influence on the aerodynamic characteristics of the golf ball.

U.S. Pat. No. 7,273,426 and U.S. Pat. No. 7,618,332 disclose a golf ball in which recesses having substantially uniform depth from the surface are formed in plural dimples with land parts therebetween, in which these recesses form patterns such as letters or graphic forms. The engraved marking to a depth that is substantially uniform can be formed simultaneously with the dimples when the cover layer of the golf ball is injection molded using a mold.

When the cover layer of a golf ball is molded, burrs can often occur at locations corresponding to the support pins and vent pins of the mold and at the seams. Because the presence of such burrs greatly worsens the aerodynamic characteristics of the golf ball, it is necessary to remove them by grinding. When the golf ball is ground to remove burrs, there is a problem in that the depth of the engraved marking formed in the surface thereof is reduced, leading to the risk of destruction of the shape of the engraved marking

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a golf ball with an engraved marking that has little influence on the aerodynamic characteristics of the golf ball, and that maintains its shape even after the surface of the golf ball is ground.

In order to achieve the above-noted object, a golf ball according to the present invention includes plural dimples provided on a surface of the golf ball; a first land part existing between the plural dimples and having as its surface a spherical surface of a sphere having the center of the golf ball as its center; a second land part having a boundary with the first land part or boundaries with the first land part and the plural dimples and having a surface having a smaller curvature than the spherical surface of the first land part; and an engraved marking disposed substantially on the second land part.

A part of the engraved marking may extend to the outside from the second land part. At least approximately 80% of the area of the engraved marking may be within the second land part. The surface of the second land part may be flat.

The changes in coefficient of drag CD and coefficient of lift CL between having and not having the engraved marking may be each within 0.005 at an initial ball velocity of 72 m/s and spin amount of 2800 rpm.

The engraved marking may include a symbol, word or a combination thereof related to golf or ball.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing the surface of a golf ball according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view along the line II-II of the golf ball shown in FIG. 1.

FIG. 3 is a plan view showing the surface of a golf ball according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view along the line IV-IV of the golf ball shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, plural dimples 12 are formed on the surface of a golf ball 10. A golf ball surface between the plural dimples 12 is generally referred to herein with regard to the present invention as a first land part 14. The first land part 14 has a spherically curved surface that is a part of a surface of an imaginary sphere 15 having its center at the center of the golf ball 10. The bottom surface of the dimple 12 is recessed from the surface of the imaginary sphere 15 and is smoothly curved from the boundary with the land part 14 toward the dimple center, which is the deepest position of the dimple 12.

In this embodiment, as shown in FIGS. 1 and 2, a second land part 16 is formed cutting away a part of the first land part 14 in a planar manner. That is, the second land part 16 has a flat surface, and the boundary between the first land part 14 and the second land part 16 is circular. Also, the second land part 16 has an engraved marking 18.

FIG. 1 shows as the engraved marking 18 the logo “Tour Stage,” which is a trademark of Bridgestone Sports Co., Ltd., but the engraved marking 18 is not restricted to this, and can include one or more symbols, including signs, numerals, letters, pictures and logos, and can include one or more words in English, or Japanese, or the like. These symbols and words may be a company name, a product name, a trademark, a name of a person, or a mascot character or the like related to golf or to balls, or one not directly related to golf or to balls. The lower limit of the area of the engraved marking 18 itself is preferably approximately 0.2 mm², and more preferably approximately 0.8 mm². The upper limit of the area of the engraved marking 18 is preferably approximately 50.3 mm² and more preferably approximately 38.9 mm².

A part of the engraved marking 18, as shown in FIG. 1, may extend to the outside from the second land part 16, but the entire engraved marking 18 may stay within the second land part 16. It is preferable that at least approximately 80% of the area of the engraved marking 18 be within the second land part 16. The area of the engraved marking means an area of a recessed part in the land part. For example, as shown in FIGS. 1 and 2, in the case in which the entire area inside the contour line of the engraved marking 16 is recessed, an area surrounded by the contour line is the area of the engraved marking 18. It is more preferable that at least approximately 90% of the area of the engraved marking 18 be within the second land part 16.

FIG. 2 shows the case in which depth of the engraved marking 18 is uniform, but the depth of the engraved marking 18 is not limited to this, and may be varied, depending upon the location of the engraved marking. The deepest point from the surface of the second land part 16 to the bottom of the engraved marking is preferably at least approximately 0.05 mm, and more preferably, at least approximately 0.1 mm. Because if the deepest point of the engraved marking is too deep, the influence on the aerodynamic characteristics of the golf ball becomes large, the deepest point is preferably at most approximately 0.2 mm and more preferably at most approximately 0.15 mm.

FIG. 1 shows the engraved marking 18 and the second land part 16 surrounded by six dimples 12, but the present invention is not limited to this. The engraved marking 18 and the second land part 16 may be surrounded by at least three dimples 12. It is preferable that the engraved marking 18 and the second land part 16 be surrounded by at most seven dimples 12.

All of the dimples 12 formed on the surface of the golf ball may be the same size, or may be of two or more different sizes. It is preferable to dispose dimples of at least three different sizes, which enables uniform and tight coverage of the entire surface of the golf ball 10.

In the case of forming dimples 12 in this manner having two or more different sizes, it is preferable that the size of the second land part 16 be larger than the largest dimple. The area of the second land part 16 is preferably at least approximately 0.2 mm² and more preferably at least approximately 0.8 mm². Because if the area of the second land part 16 is too large, the influence on the aerodynamic characteristics of the golf ball becomes great, the area of the second lamp part 16 is preferable at most approximately 50.3 mm² and more preferably at most approximately 38.9 mm². The size of the second land part is preferably larger than the smallest dimple. The maximum length of the engraved marking 18 is preferably smaller than approximately 1.2 times the maximum length of the largest dimple. The maximum length of the engraved marking 18 is the maximum distance between two points on the contour line of the engraved marking 18. The maximum length of the dimple is the diameter thereof if the dimple is circular.

Only one engraved marking 18 or two or more engraved markings 18 may be formed on the overall surface of the golf ball 10. The number of dimples 12 surrounding the one or more engraved markings 18 is preferably at most approximately 30% of the total number of dimples formed on the surface of the golf ball. For example, in the case in which the total number of dimples is 272, it is preferable that the number of dimples surrounding the engraved marking be at most 82. Thus, for example, in the case in which the number of dimples surrounding one engraved marking is selected as four, it is possible to form from 6 to 20 engraved markings. In particular, the number of dimples 12 surrounding one or more engraved markings 18 is preferably at most approximately 10% of the total number of dimples. For example, in the case in which the total number of dimples is 272, it is preferable that the number of dimples surrounding the engraved markings be at most 27. Thus, for example, in the case in which the number of dimples surrounding one engraved marking is selected as five, it is possible to form from 1 to 5 engraved markings.

The total number of dimples formed on the golf ball surface is preferably at least approximately 150, more preferably at least approximately 200, yet more preferably at least approximately 250, and still more preferably at least approximately 300. Also, the total number of dimples is preferably at most than approximately 500, more preferably at most approximately 400, and still more preferably at most approximately 360.

FIG. 1 shows only circular dimples 12, but the present invention is not limited to this. A non-circular dimple, which has a boundary line between the dimple and the land part formed by a curved part and a linear part, may be formed together with the circular dimples.

As described above, because the engraved marking 18 is either substantially the same size as or smaller than a dimple and also has a shallow depth, the engraved marking 18 has little influence on the aerodynamic characteristics of the golf ball 10. It is preferably that, when the ball is struck with an initial ball velocity of 72 m/s and a spin amount of 2800 rpm, the differences between the coefficient of drag, CD₀, and the coefficient of lift, CL₀, for a ball without engraved markings and the coefficient of drag, CD₁, and the coefficient of lift, CL₁, for a ball with engraved markings be within 0.005.

In the process of manufacturing a golf ball, the second land part 16 and the engraved marking 18 can be formed in the process step of forming the cover layer of the golf ball. Specifically, the cover layer is formed by injection molding of the cover layer material into a mold. The cover layer mold has a cavity wall surface for the purpose of forming the surface of the first land part, concave parts protruding from the cavity wall surface for the purpose of forming dimples, and flat parts for the purpose of forming the second land part. A protrusion for forming the engraved marking is provided on the flat surface for forming the second land part. By using a mold such as this, it is possible to mold the golf ball having the engraved marking 18 on the flat surface of the second land part 16.

After the golf ball is molded using the mold, the entire surface of the golf ball is ground to remove the burrs that formed on the surface. A conventional grinding method can be used. Because the engraved markings 18 are formed in the second land parts 16 that are lower than the surface of the first land parts 14, it is possible to maintain the shape of the engraved marking 18 by preventing the grinding of the surface of the second land part 16, when the surface of the golf ball is ground.

The present invention is not limited to the above-noted embodiment, and may also include a golf ball 20 in another embodiment, which is shown in FIGS. 3 and 4. Whereas in FIGS. 1 and 2 the planar shape of the second land part 16 is circular, for example, the surface of the second land part 26 of the golf ball 20 can be made as a surface formed by cutting away the spherical surface of the first land part 24 and edge parts of the dimples 22 therearound, as shown in FIGS. 3 and 4. That is, the second land part 26 can have, in addition to a boundary with the first land part 24, a boundary with the dimples 22. By designing the second land part 26 in this manner, it is easy to dispose an overall engraved marking having a desired shape on the surface of the second land part 26.

Also, whereas in FIGS. 1 and 2 the surface of the second land part 16 is flat, it is possible, as shown in FIG. 4, to impart to the second land part 26 a shape that curves outward toward the outside of the golf ball. This curved surface has a smaller curvature than the spherical surface 25 of the first land part. By forming an engraved marking 28 in the curved surface of the second land part 26 in this manner, it is possible to maintain the shape of the engraved markings 28 by preventing the grinding of the surface of the second land part 26, when the surface of the golf ball is ground.

Additionally, whereas in FIGS. 1 and 2 the engraved marking 18 is formed so that the entire inside of the contour line thereof is recessed from the surface of the second land part 16, the engraved marking 28 can be formed, as shown in FIG. 4, so that the contour part 28 a thereof is recessed from the surface of the second land part 26. The region 28 b that is surrounded by the contour part 28 a has a surface having the same curvature as the surface of the second land part 26. In this case, the area of the engraved marking 28 is equal to the area of the contour part 28 a. By making the engraved marking in this manner, it is possible to reduce the area of the recessed part, and thus, it is possible to reduce the influence on the aerodynamic characteristics of the golf ball.

A molding die for manufacturing a golf ball according to the present invention may be fabricated by using 3-dimensional CAD or CAM and by using a method in which an overall surface shape is directly and three-dimensionally formed in a reversing master die, or a method in which a cavity part of the molding die is directly and three-dimensionally machined. An ionomer resin, a polyurethane-based thermoplastic elastomer, and thermoplastic polyurethane can be used as materials for the cover layer. The golf ball may be of a one-piece structure or of a multiple-piece structure having two or more pieces.

While a golf ball according to the present invention has been described in connection with preferred embodiments, it is not intended to limit the scope of the invention to the particular form set forth, and on the contrary, it is intended to cover such alternatives and modifications as may be included within the spirit and scope of the invention as defined by the appended claims. 

1. A golf ball comprising: plural dimples provided on a surface of the golf ball; a first land part existing between the plural dimples and having as its surface a spherical surface of a sphere having the center of the golf ball as its center; a second land part having a boundary with the first land part or boundaries with the first land part and the plural dimples and having a surface having a smaller curvature than the spherical surface of the first land part; and an engraved marking disposed substantially on the second land part.
 2. The golf ball according to claim 1, wherein a part of the engraved marking extends to outside from the second land part.
 3. The golf ball according to claim 1, wherein at least approximately 80% of the area of the engraved marking is within the second land part.
 4. The golf ball according to claim 1, wherein the surface of the second land part is planar.
 5. The golf ball according to claim 1, wherein the changes of a coefficient of drag CD and a coefficient of lift CL between having and not having the engraved marking are each within 0.005 at an initial ball velocity of 72 m/s and spin amount of 2800 rpm.
 6. The golf ball according to claim 1, wherein the second land part is surrounded by at least three dimples.
 7. The golf ball according to claim 1, wherein the second land part is surrounded by at most seven dimples.
 8. The golf ball according to claim 1, wherein the plural dimples comprise dimples having at least two different sizes.
 9. The golf ball according to claim 8, wherein the second land part has a smaller size than a largest dimple among the plural dimples.
 10. The golf ball according to claim 8, wherein the second land part has a greater size than a smallest dimple among the plural dimples.
 11. The golf ball according to claim 8, wherein a maximum length of the engraved marking is smaller than approximately 1.2 times a maximum length of a largest dimple among the plural dimples.
 12. The golf ball according to claim 1, comprising at least two of the engraved markings
 13. The golf ball according to claim 1, comprising one or more of the engraved markings, wherein the number of dimples surrounding the one or more engraved markings is at most approximately 30% of the total number of dimples formed on the golf ball.
 14. The golf ball according to claim 1, wherein a deepest point from the surface of the second land part to a bottom of the engraved marking is at least approximately 0.05 mm.
 15. The golf ball according to claim 1, wherein a deepest point from the surface of the second land part to a bottom of the engraved marking is at most approximately 0.2 mm.
 16. The golf ball according to claim 1, wherein the engraved marking comprises a symbol related to golf or ball.
 17. The golf ball according to claim 1, wherein the engraved marking comprises a word related to golf or ball. 